The present invention relates to an infrared radiation detector.
The infrared radiation detector is used in sensing a thermal object such as human body and measuring the temperature of the thermal object.
Detection of a thermal object by means of infrared radiation detector has a wide application for, for example, crime prevention, traffic and disaster monitoring. The use of infrared radiation detector also facilitates measurement of the temperature of a thermal object without touching the body.
The infrared radiation detectors can be roughly classified into two types: quantum detector using a photovoltaic effect and thermal detector using heat generated by infrared radiation.
Of the two detectors, the thermal detector has been attracting attention greatly because it does not depend on the infrared wavelength and because it does not require cooling despite its lower sensitivity than the quantum detector. The thermal detector is subclassified into various types according to the principle of operation; pyroelectric detector, bolometer type detector, thermocouple detector, ferroelectric bolometer type detector, etc.
Of the various thermal detectors, the pyroelectric detector has been widely applied in human detection because of high sensitivity thereof. This detector comprises, for example, an MgO substrate having microcavities formed on the surface thereof by micromachining techniques (see Journal of Applied Physics, 32, 1993, pp. 6297-6300, by Kotani et al.) and a lead lanthanum titanate (PLT) ferroelectric thin film formed on the surface of the MgO substrate (see Journal of Applied Physics, 63(12), 1988, pp. 5868-5872, by Takeyama et al.). The resistive bolometer and the ferroelectric bolometer have been used in measuring temperature because they allow determination of an absolute value of temperature by a resistance and a dielectric constant.
Recently, there is a proposal of an tympanic thermometer using the thermal detector. The tympanic thermometer can measure the temperature of a subject in a short time by simple insertion of the thermometer into the host's ear. The detection mechanism of the tympanic thermometer is as follows: A sensor mounted in the thermometer senses infrared ray by a pyroelectric effect. The sensor detects a difference between the temperature of a piezoelectric chopper and that inside the ear. The temperature of the piezoelectric chopper is detected by a contact thermistor mounted on the pyezoelectric chopper in the thermometer. The difference between the temperature of the piezoelectric chopper and that of the ear is calculated, and a sum of the chopper's temperature and the temperature difference is output as the temperature of the subject.
In a practical thermal sensing system, a combination of plural different infrared radiation detectors may be used in order to have a desired function. For example, two infrared radiation detector units, one for detecting the presence of a thermal object and one for measuring the temperature of the detected thermal object, may be formed in a single system. For the infrared radiation detector unit for detecting a thermal object, either the pyroelectric detector or the ferroelectric bolometer utilizing a field-enhanced pyroelectric effect may be used. For the other for measuring the temperature of a heat source (thermal object), the resistive bolometer or the ferroelectric bolometer may be used.